The present invention relates to a method for activating coal for use as an adsorbent, the activated coal and a method of adsorbing impurities from effluent gases using the activated coal. The invention finds particular utility in the adsorption of SO.sub.2 from effluent gases.
It is well known that substantial quantities of sulfur dioxide are released into the air each year by the burning of sulfur-containing coal and oil and the refining of oil and various metals. Sulfur dioxide concentrations of only a few parts per million (ppm) in air can cause breathing difficulty, kill plants, and accelerate the deterioration of paper, leather and limestone building materials. Therefore, federal, state and local governments have placed restrictions on the amount of SO.sub.2 which can be discharged into the atmosphere.
In an effort to remove sulfur dioxide from effluent gases, various forms of carbon have been suggested as adsorbents. For example, Ninomiya et al, U.S. Pat. No. 3,544,263, discloses that it is known that sulfur dioxide can be removed from gases with metallic oxides such as vanadium oxide, coke or conventional activated carbon. The patent describes a novel adsorbent prepared from a mixture of finely ground bituminous coal and an inorganic sodium or potassium compound. The mixture is gasified with steam, carbon dioxide, flue gas, sulfur dioxide, air or a mixture of these gases. Dimitri, U.S. Pat. No. 3,886,093 discloses an SO.sub.2 adsorbent prepared from liquid having active metal sites, such as vanadium metal sites.
A special activated coke (BF char) is used to adsorb sulfur dioxide in the Bergbau Forschung process described in P. Steiner et al, "Removal and Reduction of Sulfur Dioxides from Polluted Gas Streams," 1975 Advances in Chemistry Series, No. 139, at 180. This material is an excellent adsorbent. However, it is extremely expensive. Therefore, a less expensive material having similar adsorbtion characteristics is needed.